Endothelial cell response to the complex hemodynamic environment of the circulatory system is critical to the pathophysiological regulation of the cardiovascular system; however the mechanism by which this signal is transduced remains poorly understood. Recent in vivo evidence suggests that cells are capable of responding locally to shear stress evidenced by polarized phosphotyrosine protein expression within single cells. The goal of this proposed project is to characterize endothelial cell response to shear stress gradients in an in vitro system where the rheological conditions can be controlled and well-defined. In doing so, this project will address two key questions: can endothelial cells respond to shear stress through localized signaling, and is cell-cell contact necessary for endothelial cell shear stress response? Aim 1 will be to investigate localized endothelial cell structure and signaling in well-defined flows. Aim 2 will be to investigate the role of endothelial cell-cell contact in transducing fluid shear stress signals to the cell. Together, these aims will define the mechanisms by which cells are capable of responding locally to shear stress. This study is intended to bridge the gap between in vivo and in vitro observations of endothelial response to flow. [unreadable] [unreadable] [unreadable]